Enhancement Of The Acid Dissolution Of Mechanically Activated Pangzhihua Ilmenite

Sulfate Process is the primary manifacture method of TiO2 pigment in China. It meets a great challenge of environment protection because of its large amount of waste acid discharge and flue gas emission. In sulfate process, ilmenite is dissolved with concentrated sulfuric acid. The reaction temperature is as high as 200℃. The emission of toxic steam of sulfuric acid is unavoidable. On the other hand, high concentration of the dissolving acid makes it impossible to recycle part of the waste acid, which is produced in hydrolysis with a concentration of 20%. Digesting ilmenite with dilute acid is benefit to recycle waste acid and cut the gas emission. However, the reaction rate is very low. Mechanical activation can greatly enhance the digestion. In this work, a ball mill was used to activated the Panzhihua ilmenite. Leaching the activated ilmenite shows that suitable activation conditions are a ball/ilmenite ratio of 70:1, and φ20 mm balls. The results show that ilmenite particle size lowered with activation time in 2 hour. Particle surface area increases with prolonging milling time. X-ray diffractions of both ilmenite and activated ilmenite demonstrate that milling operation reduced the crystallite size during the first 4 hours. The lattice constant a calculated with XRD data also varied with milling time. The enhancement of leaching ilmenite is due to both shrinking crystallite size and defecting crystal lattice. Ilmenite samples milled for different times from 0 to 120 min was leached under agitating rate of 700 r/min. The results show that the apparent activation energy reduced with increasing milling time under the conditions of 400:2 acid/solid ratio, 40% sulfuric acid concentration and 80～120℃. Dissolution of ilmenite includes two stages. In the initial period, the leaching reaction was much fast. Detecting the reaction residue found that the particle size of unreacted core increased in the first 30 min and then decreased in the following period. Crystallite size calculated from XRD data dropped after 15 minutes. A multi-step liquid-phase digestion technology was tested under a condition of 1.4:1.5 of aid/solid ratio, 50% of sulfuric acid concentration and 120℃, more than 90% of total titanium extraction was obtained in 4 consecutive digests. The titanium-contained solution obtained hereby reacted with mechanically activated ilmenite at 100℃for 1 hour. Its F value drops to 2.1. It is comparable with the operation parameter in commercial process.